Enhanced performance in hybrid perovskite solar cell by modification with spinel lithium titanate

Abstract

Lithium salts have been important additives to the hole-transport materials of solid-state hybrid perovskite solar cells to achieve higher hole mobility. However, the observed intercalation of Li⁺ into TiO₂ was demonstrated to decrease the open-circuit voltage (V_OC) of the cells. In this work, spinel lithium titanate Li₄Ti₅O₁₂ (LTO) was used to alleviate this issue by consuming Li⁺ prior to the contact of Li⁺ with TiO₂ at the interface between sensitized TiO₂ and the hole-transport layer through the chemical insertion of Li⁺ into LTO. Raman and X-ray photoelectron spectroscopy results confirmed the insertion of Li⁺ into LTO. A Li⁺ insertion peak in cyclic voltammetry and an increased density of states of TiO₂ revealed the role of LTO as a Li⁺ separator to protect the TiO₂ photoanode, providing the mechanism of V_OC increase for LTO modification. Electrochemical impedance spectroscopy revealed that LTO modification markedly reduced carrier recombination, improving the fill factor of the devices. Overall, the conversion efficiencies of the devices were significantly increased with a maximum efficiency of 15.1% by addition of LTO. The strategy of using LTO as a multifunctional modifier broadens the scope of interface engineering in solar cells.